I was not involved in the choice of the XLFD suffix name *-iso10646-1,
but the ISO 8859 series comes in a number of "parts". Part 1 is commonly
referred to as ISO 8859-1. Similarly, ISO 10646 has a "Part 1", which is
"Architecture and Basic Multilingual Plane".

Since the XLFD suffix for the 8859 series is *-iso8859-1, etc, the
suffix *-iso10646-1 is actually just following that same convention. I
don't know if that was the original reason for naming it that way
though. Perhaps Markus would know. Is he at the conference?